Follicle stimulating hormone (FSH) is a heterodimeric gonadotropic hormone secreted by the pituitary gland, and is one of three anterior pituitary glycoprotein hormones including, in addition to FSH, thyroid-stimulating hormone (TSH) and luteinizing hormone (LH). FSH consists of two non-covalently bound subunits referred to as the alpha (α) and beta (β) subunits. The alpha subunit is the same amongst the three hormones, while the beta subunit is unique to each hormone and confers specificity. In humans, the mature alpha subunit consists of 92 amino acid residues and possesses two carbohydrate chains. The corresponding FSH mature beta subunit is composed of 111 amino acids and also possesses two carbohydrate chains. Together, the two subunits have a molecular weight of about 31 kD measured by mass spectroscopy and about 35–45 kD measured by PAGE or gel chromatography depending upon the state of glycosylation. FSH directly regulates the metabolic activity of granulosa cells of the ovary and Sertoli cells of the testis.
Pharmaceutical preparations of follicle stimulating hormone (FSH) play an important role in the treatment of human infertility, and administration of FSH, either alone or in combination with other biologically active compounds and proteins, has been employed for treating infertility problems since the early 1960s. In females, FSH promotes ovarian follicular development and pharmaceutical preparations of FSH are used primarily for ovulation induction and in in vitro fertilization procedures. [Speroff, L. Glass R. H., et al., Clinical Gynecologic Endocrinology and Infertibility. 583–609 (1989); Jones, H. W., et al., Fertil. Steril, 38:14–21 (1982)]. In males, such compositions are used to initiate and maintain spermatogenesis in hypogonadotropic hypogonadism [Witcomb, R. W., et al., J. Clin Enzdocrinol Metab, 70:3–7 (1990)].
In early infertility treatment methods, FSH-containing formulations were administered via injection into deep muscle. Such injections were typically given with the aid of the patient's partner or healthcare provider and required the use of a needle up to five times the size of a typical subcutaneous needle and were very painful. More recently, formulations have been developed in which purified or recombinant FSH is administered subcutaneously, often by patient self-administration. Although subcutaneously administered FSH offers an advantage over intrasmuscularly delivered drug by allowing the patient greater independence through self-administered treatment, many patients are reluctant or unwilling to undergo infertility treatments requiring the subcutaneous administration of FSH, due to the inconvenience, discomfort, or even inherent dislike associated with needle-based delivery methods.
Pulmonary delivery has received much attention as an attractive alternative to subcutaneous injection, because this approach eliminates the necessity for needles, limits irritation to the skin and body mucosa (common side effects of transdermally, iontophoretically, and intranasally delivered drugs), and eliminates the need for nasal and skin penetration enhancers (typical components of intranasal and transdermal systems that often cause skin irritations/dermatitis). Pulmonary administration is also economically attractive, amenable to patient self-administration, and is often preferred by patients over other alternative modes of administration. However, due to their high molecular weight and low lipophilicity, peptide or protein based drugs have not traditionally been among those drugs that are administered by inhalation for deposition in and absorption from the lung, although various aerosol formulations have been suggested. Moreover, a previous attempt to administer FSH in dry powder form via intratracheal delivery resulted in apparently low bioavailability—0.6 percent relative to intravenous administration—suggesting the undesirability of the pulmonary route for delivering gonadotropin hormones such as FSH [Komada, F., et al., J Pharm Sciences, 83, (6):863–867 (1994)].
Another often-encountered problem in formulating proteins for administration is their tendency towards inactivation. With the recent advent of more effective purification and recombinant techniques, highly purified forms of both urinary-derived [Arpaia, G., et. al., U.S. Pat. No. 5,128,453, Jul. 7, 1992] and recombinant [Loumaye, E., et al., Fertil. Steril., 63:77–86 (1995)] FSH have become available, making this problem even more pronounced. Although these highly purified forms of FSH offer many potential advantages over less purified forms, including improved batch-to-batch consistency, high specific activity due to the absence of luteinizing hormone and other competing proteins, improved efficacy, good local tolerance to injections, and low immunogenicity, preparations containing very pure FSH are often highly unstable. These compositions often degrade in a relatively short time, with a partial or even complete loss of bioactivity. Moreover, although excipients have been described which are capable of stabilizing FSH-containing solid formulations [e.g., Samaritani, et al., U.S. Pat. No. 5,650,390, Jul. 22, 1997] for reconstitution to injectable forms, such solid formulations typically lack the features necessary for pulmonary delivery.
Thus, even with the amount of work that has been done to optimize pulmonary delivery of proteins, there still does not exist an effective system and method of pulmonary delivery of FSH that (i) provides a sufficiently stabilized, respirable, dry powder form of FSH, (ii) eliminates the need for cold storage, (iii) provides powders having superior aerosol properties, (iv) requires neither propellants to aid in dispersion nor enhancer compounds to enhance absorption in the lower respiratory tract, and (v) exhibits good pulmonary bioavailability.